During the takeoff phase of a typical large aircraft with a tricycle landing gear, a pilot will manipulate the flight controls of the aircraft to cause the aircraft to rotate. During rotation, the aircraft pivots around the axis of its main landing gear truck, causing the nose of the aircraft to pitch up while the tail of the aircraft moves toward the ground. The aircraft will rotate about the axis until, preferably, the aircraft is at the correct rotation angle for the given aircraft design and takeoff conditions. The maximum rotation angle for any given aircraft design is limited by the distance between a portion of the aircraft under the fuselage tail section and the ground during the aircraft rotation.
Aircraft manufacturers have designed various types of landing gear to increase the distance between a portion of the aircraft under the fuselage tail section and the ground to provide a larger rotation angle. An example is a semi-levered landing gear (SLG). Conventional SLGs include a bogie beam and a main strut pivotally connected to the bogie beam to form a wheel truck. The bogie beam typically includes a forward set of wheels and an aft set of wheels, and may contain additional sets of wheels in between the forward and aft sets. The forward set of wheels and aft set of wheels are attached to opposing, distal ends of the bogie beam. A lower portion of the main strut (landing gear shock strut) is attached to a central position of the bogie beam. An auxiliary strut is also attached to the upper portion of the main strut and to the bogie beam at a position proximate to the forward set of wheels. The auxiliary strut is used in conjunction with the main strut to rotate the bogie beam about an axis at the central position.
In a typical SLG, the main strut includes a piston and oleo-pneumatic (oil-air) chamber that, when charged with a pressurized gas, will cause a main strut piston to extend and increase the length of the main strut. This main (shock) strut serves to dampen, or reduce, acceleration between the bogie beam and aircraft to reduce loads into the aircraft as well as improve comfort for people onboard the aircraft.
An advantage of a conventional SLG is that during takeoff, an aircraft using an SLG can have an increased rotation angle through the interaction of the bogie beam and the struts. As an aircraft forward speed increases, the wings will begin to lift the aircraft and the landing gear shock strut will extend. With a SLG system, the auxiliary strut does not extend as the main strut extends. This action has the effect of rotating the bogie beam about the central pivot point such that the forward set of wheels is higher than the aft set of wheels, thereby increasing the height of the aircraft and allowing greater aircraft rotation. Further, during the rotation phase of takeoff, the aircraft will rotate about an axis of the set of aft wheels rather than a central point of the bogie beam where the main strut is located. Moving the center of rotation aft also allows the aircraft to increase rotation angle.
While providing an increased level of takeoff performance over other types of landing gears, if not designed properly, SLGs can decrease landing performance. The reduction in landing performance can be attributed to an additional force acting on the main strut causing the main strut to compress and therefore lower the height of the aircraft. With the conventional SLG system, the level of oleo pre-charge pressure may be increased to minimize the shock strut compression. The increased oleo pre-charge can result in a compromise between takeoff and landing performance.
It is with respect to these and other considerations that the disclosure made herein is presented.